Center beam rail road cars generally have a rack-like body, in which there is a longitudinally extending deck and an upstanding center beam assembly running down the center of the car. The center beam structure is carried on a pair of rail car trucks. The cars have a pair of end bulkheads that extend transversely to the rolling direction of the car. The lading supporting structure of the beam includes laterally extending decking mounted above, and spanning the space between, the trucks. A center beam web structure, typically in the nature of an open frame truss for carrying vertical shear loads, stands upright from the deck and runs along the longitudinal centerline of the car between the end bulkheads. This kind of webwork structure can be constructed from an array of parallel uprights and appropriate diagonal bracing. Most often, a top truss assembly is mounted on top of the vertical web and extends laterally to either side of the centerline of the car. The top truss is part of an upper beam assembly, (that is, the upper or top flange end of the center beam) and is usually manufactured as a wide flange, or wide flange-simulating, truss, both to co-operate with the center sill to resist vertical bending, and also to resist bending due to horizontal loading of the car while travelling on a curve. Typically, a center sill extends the length of the car. The center beam thus formed is conceptually a deep girder beam whose bottom flange is the center sill, and whose top flange is the top truss (or analogous structure) of the car.
Center beam cars are commonly used to transport packaged bundles of lumber, although other loads such as pipe, steel, engineered wood products, or other goods can also be carried. The space above the decking and below the lateral wings of the top truss on each side of the vertical web of the center beam forms left and right bunks upon which bundles of wood can be loaded. The base of the bunk may include risers that are mounted to slant inward, and the vertical web of the center beam is generally tapered from bottom to top, such that when the bundles are stacked, the overall stack leans inward toward the longitudinal centerline of the car.
Lading is most typically secured in place using straps or cables. Generally, the straps extend from a winch device mounted at deck level, upward outside the bundles, to a top fitting. The top fitting can be located at one of several intermediate heights for partially loaded cars. Most typically, the cars are fully loaded and the strap terminates at a fitting mounted to the outboard wing of the upper beam assembly. Inasmuch as the upper beam assembly is narrower than the bundles, when the strap is drawn taut by tightening the winch, it binds on the upper outer corner of the topmost bundle and exerts a force inwardly and downwardly, tending thereby to hold the stack in place tight against the center beam web.
Each bundle typically contains a number of pieces of lumber, commonly the nominal 2″×4″, 2″×6″, 2″×8″ or other standard size. The lengths of the bundles vary, typically ranging from 8′ to 24′, in 2′ increments. The most common bundle size is nominally 32 inches deep by 49 inches wide, although 24 inch deep bundles are also used, and 16 inch deep bundles can be used, although these latter are generally less common. A 32 inch nominal bundle may contain stacks of 21 boards, each 1½ inch thick, making 31½ inches, and may include a further 1½ inches of dunnage for a total of 33 inches. The bundles are loaded such that the longitudinal axes of the boards are parallel to the longitudinal, or rolling, axis of the car generally. The bundles are often wrapped in a plastic sheeting to provide some protection from rain and snow, and also to discourage embedment of abrasive materials such as sand, in the boards. The bundles are stacked on the car bunks with the dunnage located between the bundles such that a fork-lift can be used for loading and unloading. For bundles of kiln dried softwood lumber the loading density is taken as 1600 to 2000 Lbs. per 1000 board-feet.
It has been observed that when the straps are tightened, the innermost, uppermost boards of the topmost bundle bear the greatest portion of the lateral reaction force against the center beam due to the tension in the straps or cables. It has also been observed that when these bundles bear against the vertical posts of the center beam, the force is borne over only a small area. As the car travels, it is subject to vibration and longitudinal inertia loads. Consequently the plastic sheeting may tend to be torn or damaged in the vicinity of the vertical posts, and the innermost, uppermost boards can be damaged. The physical damage to these boards may tend to make them less readily saleable. Further, whether or not the boards are damaged, if the plastic is ripped, moisture can collect inside the sheeting. This may lead to the growth of molds, and may cause discolouration of the boards. In some markets the aesthetic appearance of the wood is critical to its saleability, and it would be advantageous to avoid this discolouration.
In part, the difficulty arises because the bearing area may be too small. Further, the join between the upstanding web portion of the center beam and the upper beam assembly can coincide with the height of the topmost boards. This join is not always smooth. Further still, when the posts are fabricated the flanges may not stand perfectly perpendicular to the web, such that one edge of the flange may bear harder against the bundles than another.
It is also desirable that the bundles stack squarely one upon another. Although it is possible to use wooden battens at the top end of the center beam web, this will tend to cause the top bundle to sit outwardly of its neighbours. It has been observed that a thin wooden batten, of ¾″ thickness may tend to bow inwardly between adjacent posts, and may not spread the wear load as much as may be desired. A 1½ inch thick wooden batten may have a greater ability to resist this bowing effect. However, the space available for employing a batten may tend to be limited by the design envelope of the car. Inasmuch as it is advantageous to load the car as fully as possible, and given that the design of the car may usually reflect a desire to maximize loading within the permissible operational envelope according to the applicable AAR standard, the use of a relatively thick wooden batten may tend to push the outside edge of the top bundle outside the permissible operational envelope. Wooden battens may also be prone to rotting if subject to excessive exposure to moisture, or may be consumable wear items that may require relatively frequent periodic replacement.
It would be desirable to have an upper beam assembly that is integrated into the structure, that is formed to spread the bearing load across a larger area, that would tend to resist the bowing phenomenon, that would tend not to require frequent replacement, and that would tend not to be prone to rotting.
Existing center beam cars tend to have been made to fall within the car design envelope, or outline, of the American Association of Railroads standard AAR Plate C, and tend to have a flat main deck that runs at the level of the top of the main bolsters at either end of the car. In U.S. Pat. No. 4,951,575, of Dominguez et al., issued Aug. 28, 1990, a center beam car is shown that falls within the design envelope of plate C, and also has a depressed center deck between the car trucks. It would be advantageous to be able to operate center beam cars that exceed Plate C and fall within AAR Plate F, with a full load of lumber in bundles stacked 5 bundles high. A five bundle high load of 33 inch bundles requires a vertical clearance in the left and right hand bunks of at least 165 inches. This significantly exceeds the vertical loading envelope of a plate C car.
In known center beam cars, such as those shown in U.S. Pat. No. 4,951,575 and in U.S. Pat. No. 4,802,420 of Butcher et al., issued Feb. 7, 1989, the deck structure of the cars has included inwardly tapering risers mounted above the cross bearers, with longitudinally extending side sills running along the ends of the cross-bearers. The side sills have been angle or channel sections. In U.S. Pat. No. 4,951,575 the side sills are z-sections with the upper leg of the Z extending outward, the lower leg extending inward, and the web between the two legs running vertically. In U.S. Pat. No. 4,802,420 of Butcher et al., the side sill is a channel section, with the legs extending laterally outward and the web, being the back of the channel, extending vertically between the two legs In both cases the winch is mounted outward of the vertical web.
In center beam cars it is desirable that the center sill be aligned with the couplers to reduce or avoid eccentric draft or buff loads from being transmitted. In dealing with lateral loads, the side sills act as opposed flanges of a beam. The loads in the side sills, whether in tension, compression, vertical shear or lateral bending, tend to be transferred to the main sill through a main bolster assembly at each end of the car. In general the bolster is located at a level corresponding to the height of the main sill, and the shear plate, if one is used, is typically at a level corresponding to the level of the upper flange of the main sill.
It is desirable to have a well deck, also called a depressed center deck or dropped deck, between the trucks, to increase the load that can be carried, and so to increase the overall ratio of loaded weight to empty weight of the car, and also to reduce the height of the center of gravity of the car when loaded, as compared to a car having a flat, straight through deck from end to end carrying the same load. In the case of a well deck, longitudinal compression and tension loads in the side sills must be carried from the level of the side sills in the well, to a second, higher level of the side sills to clear the trucks, and then through the bolster structure and into the main sill. The transmission of forces through the vertical distance of the eccentricity of the rise from the side sills height in the well to the side sill height of the end deck adjoining the bolster results in the generation of a moment. When the side sill has a knee at the transition from the well to the end structure of the car, the height of the knee defines the arm of the moment.
The centerline height of a coupler of a rail road car, when new, may be 34½″ above top of rail (TOR). This is a standard height to permit interchangeable use of various types of rail cars. The main sill, or stub sill if used, tends to have a hollow box or channel section, the hollow acting as a socket into which the coupler is mounted. The minimum height of the main sill at the trucks (or stub sill, if one is used) and end structure bolsters tends to be determined by the coupler height, and the height required to clear the wheels. The height of the well deck is limited by the design envelope, be it Plate C, Plate F, or some other. In general, however, the height of the shear plate, or top flange of the bolster, to the well decking is less than the desired 33 inch bundle height. It is desirable for the top of the first layer of bundles stacked in the well to be at a height that permits the next layer of bundles to match the height of bundles stacked over the trucks. Consequently it would be advantageous to have a false deck, or staging, mounted above the shear plate, or if there is no end structure shear plate, then above the bolster, at a level to match the level of the top of the bundles carried in the well between the trucks.
One way to reduce the stress concentration at the knee is to make the side sill section of the end portion of the sill deeper. Another way to reduce the stress concentration at the knee is to make the knee member wider. On the longitudinally inwardly facing side of the knee (that is, the side oriented toward the lading in the well) the flange of the vertical leg of the knee may tend to extend perpendicularly. On the longitudinally outboard side, that is, the side facing the truck, the longitudinally outboard flange can be angled, or swept, resulting in a tapering leg, rather than one with parallel flanges. An increase in the section width, due to tapering the longitudinally outboard flange is desirable, as it permits a reduction in the stress concentration in the side sill assembly at the knee, and tends to provide greater truck clearance.
Where a dropped deck center beam car is used, the juncture between the posts and the medial portion of the center sill may leave a discontinuity in the lading contacting surface. That is, where the center sill is a straight-through center sill, such that (subject to any cumber) the top flange of the center sill runs continuously from one end of the rail road car to the other in a single horizontal plane, the lower bundles of the lading in the medial portions of the car are nestled snug against the laterally outwardly facing bearing surfaces of the medial portion of the center sill. The upper bundles nestle against, and the load securement cables are tightened to encourage snug securement against, the laterally outwardly facing flanges of the center beam assembly posts. Due to the practicalities of manufacturing, there may be a discontinuity between the lading contacting interface surface, or surfaces, of the medial portion of the center sill and the outwardly facing flanges of the posts. This discontinuity may be deliberate—as when the center sill has parallel, vertical webs, and the posts are tapered, or it may be inadvertent, as when the posts are slightly misaligned on installation, either being angularly mis-oriented such that the join is skewed, or translationally mismatched such that the join is not co-planar, or the weld at the join may not be ground flush and smooth, leaving a protruding asperity to damage adjacent lading.
It may therefore be advantageous to have, in the medial portion of the car, posts whose flanges extend the full height from the top chord to the deck of the medial section, presenting one continuous, planar bearing surface. Such a continuous surface may tend not to have local asperities due to mis-aligned adjacent members or poorly executed and finished weldments. To achieve this objective of a continuous bearing surface, it may be desirable, as shown and described herein, to employ a center sill medial portion whose external surfaces lie shy of (or put differently, not proud of) the profile of the bearing surfaces of the posts. To that end it may be advantageous to employ a shallow center sill, as in one aspect of the present invention, in which the upper flange of the center sill is not continuously planar, but rather has a depressed medial portion lying lower than the end portions. Further, it may be advantageous to employ a shallow, or very shallow, center sill in the medial, or dropped deck portion of the car, in which the upper flange of the center sill lies at a level corresponding to, or shy of, the level of the upwardly facing lading bearing interface of the medial portion of the deck structure. For example, the upwardly facing lading bearing interface of the deck structure may be either the support array formed by the upwardly facing surfaces of a series of risers, such as may be mounted over pitched cross-members, or, in a riserless car, may by the generally flat surface of the deck in a riserless car.
Optionally, a shallow center sill as shown and described in one aspect of the invention herein, may result in an eccentric moment being placed upon the center sill, as, for example, when the car is subjected to a longitudinal squeeze (i.e., buff) load. Such a squeeze load may be idealized as a longitudinal compressive load applied at the centerline of the couplers, with the tendency to cause the center sill to buckle. Where the centroid of the cross-section of the shallow portion of the center sill (or of the medial section of the deck in a center-sill-less medial portion, should such a novel structural feature be adopted in a center beam car) lies below the centerline of the couplers, there may tend to be a moment carried through the knees. In that circumstance it may be advantageous to provide a longitudinal reinforcement member for carrying at least a portion of the squeeze load, and, additionally, it may be advantageous for that longitudinal compression (or, indeed tension) carrying member to have the centroid of its cross sectional area located at a level at or above the centerline of the couplers. In such an instance, as shown and described herein in another aspect of the present invention, the compression member spaced upwardly from the center sill would also lie within the profile of the flanges of the posts.
It may be advantageous to be able to carry loads other than, for example, bundles of lumber, on at least a part of the return journey. While this can be done with center beam cars presently in use, the overhanging wings of the top truss may tend to complicate loading of the car from above. For example, it may be more convenient to load pipe, or other objects, using an overhead crane rather than to employ side loading using a fork-lift of perhaps more limited lifting capacity. Such loading would be facilitated by removal of the top truss. Further still, in addition to removal of the top truss, truncation of the central web at a level below the bottom of the uppermost row of bundles permits the top row of bundles to be loaded side by side. Strapping for securing the load, rather than being attached to the wings of the top truss, can be carried fully over the load to the winches at deck level on opposite sides of the car. In addition, the top chord can be made wider than the posts, such that the bundles bear against the smooth outside face of the top chord at a stand-off distance clear of the flanges of the posts.
Further, where, as described in one aspect of the invention herein, the top chord is relatively narrow, and is not surmounted by a top truss structure of significant lateral extent, it may be advantageous to provide a low-abrasion cover. It would be further advantageous if that cover could be manufactured from a single piece of stock, and if it could be installed in a manner where gravity might tend aid in keeping the cover in place.
Torsional loads applied to the center beam assembly are transmitted through the trucks and reacted at the rails. A significant portion of this load is transferred into the deck and main sill structure at the longitudinal location of the truck center by the main posts that extend upwardly from the deck above the truck center. It may be that the main post is narrower than the center sill top cap (i.e., upper flange), and narrower than the underlying center sill webs. It such circumstances it may be advantageous to provide web and flange continuity in the center sill beneath the main post.